1. Technical Field
This invention relates generally to wired and wireless communication systems and more particularly to Radio Frequency power amplifiers and antennas of wireless devices and drivers of wired devices.
2. Related Art
Communication systems support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Communication systems are constructed, and hence operate, in accordance with one or more communication standards. For example, wireless communication systems operate in accordance with one or more standards including, but not limited to, IEEE 802.11x, Bluetooth, wireless wide area networks (e.g., WiMAX), advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), North American code division multiple access (CDMA), Wideband CDMA, local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), and many others. Wired communication devices operate according to respective communication standards.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations, and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). The receiver couples to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard. As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
Most, if not all wireless communication standards limit transmitted power level. Further, some wireless communication standards include reverse link power control, which allows a remote device to control transmit power of another wireless device, e.g., base station controls reverse link transmit power of hand held devices. Thus, in most if not all wireless devices, the power amplifier and preceding components is actively controlled to thereby control transmit power. Shortcomings exist with respect to the efficiency of the power amplifier. When the power amplifier is matched well with the antenna, efficient transmission results; when these components are mismatched, inefficiency results. Such inefficiency results in excess power drain (by the power amplifier) as well as reduction in transmit power. This mismatch can occur due to operational variations of the antenna, e.g., alteration of load impedance due to antenna configuration/position, as well as operational variations of the power amplifier and other RF signal path components of the wireless device due to temperature fluctuations, voltage supply variations, etc.
Antenna impedance may change based upon position of the wireless device with reference to surrounding structure. For example, when a user of a mobile wireless device picks up the device, antenna impedance as seen by a driving component, e.g., the power amplifier, changes. A change in load impedance as seen by the power amplifier typically causes the device to be less efficient, decreasing transmission efficiency and increasing battery drain. Of course, propagated signal power is also affected by changes in the load impedance, which typically results in decreased wireless communication rates, dropped calls, etc. Similar issues exist in wired communication devices with regard to wired devices and the interconnect that couples the wired communication devices to their respective wired links.